It is a sight that British vicars fear more than an empty collection plate.

The business card is deposited anonymously with the loose bills and change at the offertory. It states: "You have been visited by the Mystery Worshipper." This means a detailed review of their church will soon be posted for all the world to see at the humor site www.Ship-of-Fools.com.

Were the pews comfortable? Was the service "stiff-upper-lip, happy-clappy, or what?" How was the preaching, on a scale of 10? Was the coffee good? Did any part of the service offer a glimpse of heaven? How about a whiff of "the other place?"

Mystery Worshippers have, during the past six years, slipped unannounced into 750 pews in England, North America and, occasionally, more exotic locales.

On the pop side of the aisle, one critic in Ohio survived a Christianized version of the racy Ricky Martin hit "Livin' La Vida Loca" -- at Easter. Video clips from "The Matrix" spiced up the service.

Meanwhile, the incense swingers at St. John Chrysostom in Manchester, England, received top marks: "The thurifer was superb and was of the standard that made even the most complex of swings and twirls look smooth and effortless. ... I have to say that more perfume and less fog would be my personal taste." Ah, but the wine was thin.

Ship of Fools has corned the market on truth-is-stranger-than-fiction ecclesiastical silliness -- from "Signs and Blunders" to the "Fruitcake Zone."

Recent offerings in the "Gadgets for God" pages -- real items sold elsewhere -- included boxer shorts covered with crosses, but with the fly sewn shut. Other links yielded bobble-head dolls of the Blessed Virgin Mary and flashing cell-phone crucifix covers. In one "church organists behaving badly" report, a Scottish musician was caught playing "Send in the Clowns" as the elders processed. A Brooklyn organist snuck a few bars of "Roll Out the Barrel" into the funeral of a popular pub patron.

But the long-running "Mystery Worshipper" feature is a clue that the site has a serious side, said editor Simon Jenkins. The goal is to reach out to "people on the fringes" who are either fleeing the church or just starting the process of investigating the faith. Almost everyone knows what it is like to be a stranger in a pew.

"There is no shortage of Mystery Worshippers," Jenkins said, during a U.S. speaking tour that included a stop last week at the National Religious Broadcasters convention in Charlotte, N.C.

"I think one reason so many people volunteer to do this is that everyone can identify with the whole process of visiting a new church. Church shopping is such a pain and it kind of helps to laugh. We know what people are going through."

For many Mystery Worshippers the most challenging part of the review process is its requirement that they test the degree to which each church welcomes strangers. The instructions are clear. At the end of the service, they are asked to stand alone in the back of the church for five minutes -- looking sad and lonely. The goal is to count the number of people who approach them to chat.

Nearly 50 percent of the time, the answer is "zero."

"Clergy dread this part of our reports," said Jenkins. "It is sad to have to see the church like that. But it can be good, too. ... Like it or not, this is a chance to see what their churches really look like to those who are on the outside."

Year after year, the "friendliness factor" is the bad news. The good news, said co-editor Steve Goddard, is that the online form's request for "heavenly moments" in worship almost always leads to results.

This is not a matter of old churches vs. new, or big vs. small.

"I think the good news is that there are genuinely spine-tingling moments of spirituality happening in pews out there," said Goddard. "It doesn't matter if it's a smells-and-bells church or a rock-the-flock church. We get reports from people who find a sense of worship in all kinds of places.

"What matters is genuine reverence and a sense that people are truly seeking the presence of God. That's what the Mystery Worshippers are looking for."